1. Field of the Invention
The present invention relates to an optical element, an optical module holder including the optical element, an optical module, and an optical connector. In particular, the present invention relates to an optical element, an optical module holder including the optical element, an optical module, and an optical connector that are suitable for attenuating an amount of light coupled between an optical transmission line and a photonic element.
2. Description of the Related Art
Conventionally, a following technology is used to perform optical communication using optical fiber. In the technology, the optical fiber and a photoelectric conversion element (such as a semiconductor laser) are each attached to an optical element including an optical surface (such as a lens surface). The optical fiber and the photoelectric conversion element are optically coupled using transmission and refraction of light by the optical surface of the optical element.
In an optical communication using optical fiber such as this, the amount of light coupled between the optical fiber and the photoelectric conversion element, via the optical element, is required to be attenuated for reasons related to communication standards, security, and the like. To meet such a requirement, the optical element conventionally includes a light-absorptive material, a light-absorptive film, a diffraction grating, and the like.
Technologies disclosed in Patent Literature 1 and Patent Literature 2, for example, are known as conventional technologies related to an optical element including a function for attenuating an amount of light, such as that above.
In other words, in Patent Literature 1, a following semiconductor laser module is disclosed. In the semiconductor laser module, a concentric diffraction ring structure is formed on a lens surface of a plastic condenser lens. As a result, the semiconductor laser module can limit an output value of diffracted light.
In Patent Literature 2, an optical module including a light attenuating section is disclosed. The light attenuating section is formed by metal or a dielectric material being laminated onto a flat, glass substrate and the like by deposition or sputtering.    [Patent Literature 1] Japanese Patent Laid-open Publication No. Heisei 11-142696    [Patent Literature 2] Japanese Patent Laid-open Publication No. Heisei 11-119063
However, the conventional technologies disclosed in Patent Literature 1 and Patent Literature 2 have problems related to optical characteristics or manufacturing, such as those described below.
As the material used to form the condenser lens, Patent Literature 1 discloses the use of a plastic material to which a light-absorptive material has been added. However, when the light-absorptive material is added to the plastic material in this way, the amount of light absorbed (in other words, the amount of light attenuated) changes because of variations in the concentration of the added light-absorptive material. This causes instability in the light emitted from the optical element. Moreover, the amount of light-absorptive material to be included is required to be changed based on the transmittance of the plastic material. As a result, cost may increase.
The optical module described in Patent Literature 2 requires sputtering or deposition of the metal or lamination of the dielectric material. As a result, the manufacturing process may become complicated and cost may increase.
Moreover, in Patent Literature 2, the light attenuating section and the condenser lens are formed separately. The manufacturing process during assembly may become complicated and the cost may increase because of the increase in the number of components, thereby interfering with the desired optical characteristics being achieved.